Nano-particles are extremely important materials in different areas ranging from nano-technology, non-linear optics, diode lasers, smart sensors, markers in drugs, gene sequencing to catalysis. Nano-materials can be obtained by various chemical and physical methods. Some examples of physical methods are vapour deposition, lithographic processes and molecular beam epitaxy (MBE). Chemical methods include the popular borohydride and citrate reduction methods for the preparation of colloidal metal (like gold, silver etc.) particles. Reference may be made to D. A. Handley, Colloidal Gold: Principles, Methods and Applications; Hayat, M. A. Editor, Academic Press, San Diego, Calif. 1989; Vol. 1, Chapter 2, wherein details of such chemical routes are given. Reduction of metal ions by radiolysis is also conventionally used for preparing nano-sized metal particles. However, the methods mentioned above suffer from drawbacks such as being environmentally hazardous (chemical methods) and result in the quick agglomeration of nano-particles leading to big particles for poor monodispersity.
Although specific capping agents are used in some of the abovementioned methods to restrict the size of the colloidal metal particles and to stabilize the particle size distribution, this makes the whole system quite complicated and user unfriendly. Another disadvantage, particularly of the radiolysis method, is that it is quite complicated and gamma ray sources are not readily available.